Electric induction furnace



Oct. 20, 1931. E F NQRTHRUP 1,828,291

' ELECTRIC INDUCTION FURNACE Filed Nov. 25, 1929 '2 Sheets-Sheet 1 Oct. 20, 1931. E. F. NORTHRUP ELECTRIC INDUCTION FURNACE Filed Nov. 23, 1929 2 Sheets-Sheet 2 i of furnaces and to a group of furnaces.

Patented Oct. 20, 1931 I UNITED STATES PATENT OFFICE EDWIN FITCH NORTHRUP, OI PRINCETON, NEW JERSEY, ASSIGNOR T'O ELECTRO- THERMIC CORPOBATION OF AJAX FARE, NEW JERSEY, A CORPORATION OF NEW JERSEY ELEC'IlRIC INDUCTION FURNACE Application filed November 23, 1929. Serial No. 409,315.

My invention relates to economy in the use of condensers in carrying on operations in a plurality of-furnaces whose power factor the condensers are intended to correct.

The purpose of my invention is to shift a main bank of condensers from one 'furnace'to another to afford power factor correction where the greater condenser need occurs, maintainin the power. factor correction of 10 the other Furnace orfurnaces by less condenser capacity, preferably constantly located across the condenser circuits.

A further purpose is to apply the same ca- I pacity to local power factor correction at .151 will of any of a pair or a group of furnaces.

Further purposes will appear in the specification and in the claims.

My invention relates both to the processes or methods involved and to apparatus by 0 which the processes or'methods may becarried out.

In the drawings I have illustrated but two applications of my invention, presenting the same form but applied respectively to a pair rom ' among various arrangements which could be utilized to carry out my invention I have selected the practical and effective form primarily because of its excellence in illustrating the principles ofmy invention.

Figures 1 and 2 are diagrammatic illustrations of the application of my invention which are identical except that Figure 2 shows the application of the invention to a larger number of furnaces than are seen in Figure 1. v,

In the drawings similar numerals'indicate like parts.

The furnace coils 5 .andfi in Figure 1, are intended to illustrate the operating coils of inductive electric furnaces of an type in which power factor correction is e ected by the use ofcondensers.

The inductor coils only of these furnaces are shown for the reason that my invention concerns the supply of current to and resonation of these coils under different 0 rating conditions and is not affected by ot'er furnace constructions and arrangements except as these affect the coils. The ooils are fed from supply lines 9 and 10 through any suitable connections by which the current can be applied across the desired number and location of turns of the coil, and by which the span of the power input connections may be varied as needed.

The connection is effected in 'tion by applying the current to the coil terminals 11, 11, at one end, and to taps illustrated as 12, 13, 14, 15, 16; 12', 13', 14', 15, 16; whereby energy supplied to the coil may be varied and the voltage across the terminals of the coils may be correspondingly changed.

In normal operation of individual furnaces of the coreless inductor type, for example, it has been customary to correct the power factor of the furnace inductor by a variable condenser bank such as 17 thrown across the terminals and changed automatithe illustra cally, or by hand, to increase the capacity as g the inductance reduces so that the power factor of the current supply for the furnace coils may be maintained substantially at unity. The tuning or resonating of these coils has involved an equipment of condensers for each furnace capable of taking care of the largest capacity required to resonate the furnace at a minimum furnace coil inductance.

It has been proposed, to effect an approximate or average tuning only at the individual furnaces and to apply the remaining capacity for tuning across the current supply for a bank of furnaces, permitting the surplus available capacity of one or more furnaces having leading power factor to be used to assist in resonating the inductance of one or more furnaces having a lagging power factor. While this effects a decided saving in capacity as compared with the total fur nace capacity which would be required to individually resonate for the inductance of each individual furnace, the saving has been very much less thancan be secured by the 4 to the pair of furnaces tion in description and not in limitation as' ticipated variations in the inductance of the.

' coil 5 or 6.

For convemence in reference the connections for applyingthe'power input and forincluding the condensers in parallel will be described as shown, as comprising for any given furnace main switches 19 and 20, conductors 21, 22, 21, 22 therefrom, conductors 23, 24 and 25, 23, 24' and by which the lines are connected with the two ends each of the coils 11, 11 and 26,26. The switches 28, 29, and 31 connect the lines with any one 215 of the taps 12 or .12, 13 or 13, 14, or 14', 15 or 15' and 16, or 16'. w

, Switches 32, 32 permit added inductances 33, 33', to be included or excluded within the path of'the corresponding conductors 24 and 30 25,24 and 25 i Switches 34 and provide for application of the. capacity 17 alternatively to whatever furnace is to receive large power input, whereby its furnace coil as 5 in the illustrations, will be resonated by the combined capacities whereas the other furnace coil or other furnace coilswhatever their numberare intended to be resonated during this time each by its capacity 18-, 18'.

In Figure 2 four furnaces are shown which add additional parts corresponding to the parts of the two furnaces shown including capacities 18 18 switches 19 19 and 20 and 20 conductors 21 ,21 22 22 23 23 243, 2 1 25 25 connecting with'the ends of the coils at 11 11 26 26 and switches 27 27 28 28 29 ,39 30 30 and 31 .31 by which connection is made to taps 12 12 13 13 14 ,11 ,15 15 and 162, 16 a The switches 32 and 313 permit addedinductances 33 and 33 to be included.

At low power inputs the variation of the input in different furnaces, or at different times and for different operations in the esame furnace need ordinarily not vary sufficiently to require that the capacities 18, 18', 18 and 18 be made adjustable, this being a matter which depends upon the character of the operations performed, the design of C3 the furnace, and the desire or opinion of the designer.

The capacities 17 and 18, 18, 18 18 are so proportioned that not only shall the capacity 17 and anyone of'the 18 group together. be

sufiicient for the maximum/capacitive requirements of an individual furnace but that the capacities 18 and18', etc. shall be sufficient to resonate each its individual furnace coil under conditions of reduced power operation, corresponding for instance to holding the charge, settling, metallurgical treatment or pouring.

The power input for settling or other operations may be but a fourth or a third of that required for melting and major furnace operations. By utilizing added inductance (33, 33, etc.) in series with the corresponding furnace coil during the settling, treating and holding operations within its furnace I amable not only to cut down that part of the voltage from the main power source which is applied to the furnace sufficiently input can conveniently be supplied from the same leads but the increase in inductance reduces the capacity required to resonate the circuit, permitting use of small capacities at 18, 18, etc. This determines that the capacities 18, 18', etc., shall be small ascornpared with the capacity 17. i

In operation, the coils of a pair of furnaces, for example, as in Figure 1, are connected as shown in that figure, providing for a melting or superheating operation, let us say, at the left within coil 5 and a metallurgiciilsor holding operation at the rightwithin col The system of taps provided may permit wide variation in the actual amount of power input with the application of condenser capacity 17, all for present purposes being classed as major power input connections. In the figure at the left the closing of switch 30 applies the line voltage across substantially tht entire inductor coil, resulting in actual power input considerably below the possible maximum power input with the condenser 17 connected as shown and providing for considerable increase in power by the application of the current at other taps than the tap 15.

minor power input operations the taps permit considerable variation in the actual power lnput applied. Whatever the tap con-- In the meantime inductance is added to the furnace coil circuit in each of the other fur-,

naces of the pair or set by inclusion of its corresponding inductance 33, 33 or 33,

which, in'the diagram, is effected by opera- .tion of its switch 32', 32 or 32 Each other furnace coil than 5 isthen resonated wholly by its individual capacity, whch no longe spans t-he furna'ce'coil alone but spans the furnace coil and added inductance.

The connections of the "different furnace coils utilizing low power input have been Both in what might be called major and.

without loss of energy so that the low power nace coil by the use of different taps,

of furshown as bridging different lengths merely to show the variation of connection perwith that in Figure only by the size ofits individual inductance bridging of different probut by the variant 7' portions of the furnace coils permissible by connection to different furnace taps.

It will be further evldent that the miniinput in ,a given furnace with use of capacities 17 and 18 for resonation may approach as closely to the maximum power input, when the capacity 17 is not used, as may be desired in the design of the furnaces by the expedient of increasing the range in variation of power input through tap connection; keeping in mind that the approach of the maximum power input when condensers 17 are omitted to the minimum of power input when condenser 17 is utilized will mean corresponding increase in the capacity of condensers 18 as compared with the capacity of condenser 17. k

It will be further evident that any ratio or proportion desired may be maintained in each individual furnace between the added inductances and the inductance of the furnace coil.

It will be further evident that application of my invention to furnaces will not interfere with operation of the furnaces in other particulars; that the furnace coil need not be changed from existing coils; and that any other furnace connection may be used as in the case of existing coils'having current supply at the voltageapplied.

It will further be evident that though the furnaces shown in my several figures are in parallel my invention does not depend upon the fact that the furnaces are in parallel.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless mumpower become evident to others skilled in the art,

to obtain part or all of the benefits of my invention Without copying the structure shown, and far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention what I claim as new and desired to secure by Letters Patent is:

1. The method of operating'a plurality of induction electric furnaces and tuning their I utilizing the lesser part of the resonating I, therefore. claim all such in so coils with a minimum of compensative capacity, which consists inutilizing a main capacity adapted for use, alternatively, with any of the furnaces along with capacity individual to each furnace to make up the complete compensative capacity for a furnace 'operating under maximum load, shifting the main capacity from furnace to furnace to meet the maximum load conditions of the different furnaces in turn, and at lower loads in the individual furnace in adding inductance to the furnace coil circuit to a suflicient extent' for the individual compensative capacity totune the individual furnaces at these lower loads. 2. The method of tuning a plurality of induction furnaces at maximum and minimum loads with a minimum of compensative capacity, which consists in utilizing condenser capacity individual to the inductors of. the several furnaces at all times for compensative capacity, in supplementing this capacity with condensers adapted for use, alternatively, with any of the furnaces, in adding inductance to the inductor circuit of each. furnace in turn, as the operating cycle of that furnace requires lower power input, to reduce the voltage applied to'the coil-and to make it possible for the capacity individual to that furnace to resonate the inductor'coil with the added inductance.

3. The method of operating inductor coil furnaces with a minimum of resonating capacity, which consistsin dividing the capacity required for resonation at maximum load in each furnace into two parts, one providing for a major part of the power input and the other for a lesser part of the power input, in shifting the major resonating capacity from one furnace to another so that it is in circuit during times of major input operation of the furnace to which the capacity is shifted, in

addition of inductance to the circuit and in pacity across the furnace and across the added inductance to resonate the furnace coil during operation furnace inputs and when the major part of the capacity is being utilized for resonance of another furnace.

4. The method of resonating a furnace coil under conditons of major and minor power input, which consists in utilizing capacities in parallel across the furnace coil for resonance with major power input and in utilizing part of the capacity only across the furnace coiland added inductance to resonate with lesser power inputs. v 6

The method of reducing the power in-' put and the capacity required for resonating the inductor coil of an induction furnace,

which consists in adding inductance in series of the furnace at lower ing the ity adaptedfto be thrown across either c011 at v will, capacities, one individual a to each furnace; adapted to assist inresonating the, inductance of the furnace coil at larger loads, and added inductance adapted to be inserted in series with each inductor at lower furnace 'loads for the purpose of reducing the voltage applied to the furnace and of permitting the individual 8. An induction furnace having an inductor coil, an inductance in series with the coil and a capacity resonating the circuit embodyinductorcoil and the inductance;

9. In a coreless induction furnace, a furnace coil, a main adjustable power-factorcorrective capacity for the coil, means for applying energy across different coil lengths at will, an added inductance capable-of inclusion in series with the coil to-reduce the voltage applied to the coil for lower furnaceloads and a capacity suited to resonate the inductor coil and added inductance.

10. In a coreless induction furnace, a furnace coil, a main capacity adapted to resonate the coil, an added inductance capable of inclusion in series withthe coil to reduce the voltage applied to the coil for lower furnace loads,-and a capacity-suited to resonate the inductor coil and added inductance, assisting the-main capacity to resonate the inducclizor coil when the added inductance is not use 11. In a coreless induction furnace, a furnace coil having taps, a main power-factorcorrective capacity for the coil, an added inductance capable of inclusion in series with the coil to reduce the voltage applied to the coil for lower furnace loads, a capacity suited to resonate the inductor coil and added inductance and a source of alternating current supply adapted to span parts of the coil to different taps.

12. In a coreless induction nace coil having taps, adapted to largely resonate the coil, an added furnace, a furinductance capable of inclusion in series with" the coil to reduce the voltage applied to the coil for lower furnace loads, a capacity suited to resonate the inductor coil and added inductance and assisting the main capacity to resonate the inductor coil-whenthe added inductance is not used and a source of current for the coil varied by the taps in extent of coil spanned.

capacities to resonate the complete inductance at the lower loads.

a main capacity 

